Various methods are known in the art for optical 3D mapping, i.e., generating a 3D profile of the surface of an object by processing an optical image of the object.
Some methods are based on projecting a laser speckle pattern onto the object, and then analyzing an image of the pattern on the object. For example, PCT International Publication WO 2007/043036, whose disclosure is incorporated herein by reference, describes a system and method for object reconstruction, in which a coherent light source and a generator of a random speckle pattern projects onto the object a coherent random speckle pattern. An imaging unit detects the light response of the illuminated region and generates image data. Shifts of the pattern in the image of the object relative to a reference image of the pattern are used in real-time reconstruction of a 3D map of the object.
Other methods use pulsed modulation in order to measure time of flight of light from an object to a detector. For example, U.S. Pat. No. 6,100,517, whose disclosure is incorporated herein by reference, describes a camera for creating an image indicating distances to points in objects in a scene. A modulated source of radiation, having a first modulation function, directs radiation toward a scene. An array detector, having a second modulation function, different from the first modulation function, detects radiation from the scene. A processor forms an image having an intensity value distribution indicative of the distance to each of the points in the scene based on the detected radiation.
Yet another method for distance mapping is described by Iizuka in “Divergence-Ratio Axi-Vision Camera (Divcam): A Distance Mapping Camera,” Review of Scientific Instruments 77, 045111 (2006), which is incorporated herein by reference. Two similar infrared (IR) light-emitting diodes (LEDs) are installed for illuminating the same object, one in front of an IR charge-coupled device (CCD) camera and the other behind the camera. One snapshot is taken of the object lighting only the front LED, and another lighting only the back LED. The ratio of the intensities of the two images is used to calculate the distance to the object, based on the decay of the intensities with distance due to the divergence of the light.